No rerack metal plating of electrically nonconductive articles

ABSTRACT

No rerack process for the metal plating of electrically nonconductive articles or objects on vinyl plastisol-coated plating racks, involving contacting the rack prior to racking thereon the nonconductive articles destined to be plated with a liquid lower alkyl formamide, preferably N,N-dimethylformamide, or N-methyl-2-pyrrolidone, or a mixture thereof, for a time sufficient to render the rack substantially nonsusceptible to electroless deposition of metal thereon during a subsequent electroless metal plating step. Consequently the prior requirement of reracking of the articles on clean racks subsequent the electroless metal plating step and prior to the electroplating is eliminated.

I United States Patent l 13,619,243

72] Inventors A. Brindisi, Jr. [56] References Cited :1 lson; TheophilJ. Wieczorek, West Haven, both UNlTED STATES PATENTS of Con 3,443,9885/l969 McCormack et al. 1 17/47 A PP 12,134 Primary Examiner-Alfred L.Leavitt Filed 1 1970 Assistant Examiner-Janyce A. Bell Patented 9, 1971Attorneys-Elwood J. Schaffer and Roger J. Drew 73] Assignee EnthoneIncorporated New Haven, Conn.

ABSTRACT: No rerack process for the metal plating of electricallynonconductive articles or objects on vinyl plastisolcoated platingracks, involving contacting the rack prior to 0 RERACK METAL PLATING 0Frzllctkigg threreqn t lzlel HOIICOIIISUICFVC arti gles deitiniq t; IlieELECTRICALLY NONCONDUCTIVE ARTICLES e a a y v dimethylformamide, orN-methyl-Z-pyrrohdone, or a mixture 23 Claims No Drawmgs thereof, for atime sufficient to render the rack substantially 52] US. Cl 117/47 A,nonsusceptible to electroless deposition of metal thereon durl7/5.5, ll7/62.l, l l7/l60 R, 204/30 ing a subsequent electroless metal platingstep. Consequently :51] lnt.Cl B44d 1/092 the prior requirement ofreracking of the articles on clean :50] Field of Search 1 17/47 A, rackssubsequent the electroless metal plating step and prior to theelectroplating is eliminated.

BACKGROUND'OF THE INVENTION- I. Field of the Invention This inventionrelates to metal plating and more particularly to a process forthe metalplating of an electrically nonconductive articles or object on aplastisol-coated rack; usually a vinyl plastisol-coated rack, whicheliminates any substantial deposition of metal on the rack. Thisinvention'also relates toa no rerack process for metal platingnonconductive articles or objects wherein the'articles are retained onthe same rack during the entirety of the process, and without therequirement of reracking the articles or objects on clean racks afterthe electroless metal plating and before the electroplating.

2. Description of the Prior Art In the prior art the plastic articles orparts to be electrolessly metal plated were usually sensitized byimmersion in a sensitizer solution, such as a stannouschloride-containing acid' aqueous solution, prior to activatingthearticles. By reason of this sensitizing prior to activation theinsulating coating of the plastisol-coated plating racks, which wasusually a vinyl polymer coating, also became metallized. This requiredreracking of the parts on clean racks prior'to'electroplating-so. as toprevent wasting of plating metal and to obtain" proper platedistribution on the articles. However, the need to rerack the articlesor parts on clean racks wastime consuming and costly.

In an effort to prevent or inhibit electroless metal plating of thevinyl plastisol-coated racks the racks weretreated heretofore in achlorinated solvent, for instance trichloroethylene. However thisresulted in severe and permanent damage-to the plastisol coating.

Additional curing of the plastisol-coated racksto prevent metal platingthereof during the electroless metal plating may be effective for a fewdays after which the racks again are metal plated during the electrolessplating. Further the danger of overcurin'g is attendant with theadditional curing, with overcuring destroying desired physicalproperties of the plastisol of the rack coating.

OBJECTS OF THE INVENTION A primary object of this invention is toprovide a new and improved process for metal plating plastic articles orobjects on plastisol coated racks otherwise susceptible to electrolessmetal plating deposition thereon, which eliminates the necessity ofreracking the articles on clean racks after the electroless metalplating and prior to the electroplating.

Ancillary objects and advantages will be readily apparent as theinvention is hereafter described.

SUMMARY OF THE INVENTION In accordance with the present invention, ithas been found that a electrically nonconductive article, object orpart, for instance plastic articles, objects or parts, can be metalplated while racked on a plastisol-coated plating rack, usually a vinylplastisol-coated rack without any substantial deposition of metal on therack during the electroless plating step. This elimination of anysubstantial electroless deposition of metal on the rack which isotherwise susceptible to electroless plating deposition of metal thereonis accomplished in accordance with the invention by contacting theplastisol coated rack, prior to racking the electrically nonconductivearticle or articles destined to be metal plated thereon, with a liquidmaterial such as a lower alkyl formamide, 'e.g. dimethylformamide, N-methyl-Z-pyrrolidone, or a mixture of the lower alkyl formamide andN-methyl-Z-pyrrolidone. Depending on the particular material or compoundutilized for such contacting of the rack, the compound can be in liquidsolution, for instance an aqueous solution of the compound, or theanhydrous compound per se. The contacting of the plating rack with suchtreatment liquid is effected for a time sufficient to render theplastisol-coated rack substantially nonsusceptible to the electrolessdeposition of metal thereon during a subsequent chemical reduction metalplating step. The nonconductive article or articles or be plated arethen racked onthe thustreated' rack followed'by activating thenonconductive article or articles and electrolessly metal plating theracked article by contacting the article with a chemical reduction metalplating solution until a metalplating of the desired thickness isdeposited on'the-article-surface, or until the article surface isrendered electrically conductive; This electroless metal plating 0 ofthe racked article'or articles occurs without any substantial metalplatingof the rack. The thus-plated article or articles still on thesamerack can'then be-and usually are electroplated, to deposit one or moremetal electroplate layers overthe electroless metal plate. By virtue-ofthe contacting treatment of the rack with thealkyl formamideorN-methyl-Z- pyrrolidone in accordance with this invention, there iseliminatedthe prior requirement of having to rerack the articles onclean racks after theelectroless metal plating andprior 1 to theeiectroplatingrThe vinyl polymer of the plastisol'coating ofthe rack isusuall'ypolyvinyl chloride and the plastisol;

coating is over the structural members of the rack which are usuallymetallic structural members.

Th'e'contactin'gof the plating rack with the'lower alkyl formamide orN-methyl-2- -pyrrolidone is usually by immersing the rackin a liquidbath or pool of the-anhydrous compound or a suitables'oiution thereof,usually anaqueous solution of the compound. However-such contacting maybe effected by spraying, pouring or in any other'suitable manner. Acontact.

time of the vinyl plastisol-coated rack with the preferreddimethylformamide'herein of 1-2 minutes renders the rackimmune or exemptfrom metal plating deposition for one complete plating cycle throughthefinal electroplating step.

Contact times of about30-60minutes of the vinyl'plastisol. coated rackwith dimethylformamide renders the rack immune or exempt frommetalplating deposition for24 hours and longer. With the longer contacttimes, there may be a slight swelling of the vinyl coating of the rack.Contact times of the vinyl plastisol-coated rack withN-methyl-Z-pyrrolidone, also a preferred treating agent herein, forabout 15-30 minutes renders the rack immune from electroless platingdeposition of metal thereon for at least'on'e complete plating cyclethrough the final electroplating step.

The present invention is primarily intended for use on plastisol-coatedracks in an intermediate stageof their life and which have developedthrough use a susceptibility to plating metal thereon during theelectroless plating step. Thisinvention may not be advantageousfor useon new plastisol-coated racks or on old racks inasmuch as such racks maynot be susceptible to metal plating deposition during the electrolessplating step. Of course if it is desired to use the present invention onnew and old racks, this is considered within the inventions scope.

The contacting of the plastisol-coated rack with the liquid lower alkylformamide and/or the liquid N-methyI-Z-pyrrolidone can be carried out atroom temperature, except when such compound is a solid in which eventthe solid is preheated intoliquid form. During the contacting treatmentof the rack, the" liquified solid or liquid mixture containing same maybe heated gently to maintain it in liquid phase. a

When' a mixture of the lower alkyl formamide and N- methyl-Z-pyrrolidoneis utilized herein to treat the plastisolcoated rack, the compounds canbe employed in the liquid mixture in any desired suitable ratio. Whethersuch compounds are utilized in the mixture in anhydrous or substantiallyanhydrous state or in aqueous solution will be dependent on theparticular lower alkyl formamide utilized. The preferred N,N-dimethylformamide and N-methyl-Z-pyrrolidone are utilizable in themixture in anhydrous or substantially anhydrous forms, or inaqueousformamide, both the N, N-diethyi formamide and N-methyl-Z-pyrrolidoneare utilized in anhydrous or substantially anhydrous form.

The lower alkyl formamide of this invention can usually be presented bythe following formula:

wherein the Rs each represent an alkyl group containing from one to fourcarbon atoms or a hydrogen atom with the proviso that at least one R isa l-4C alkyl group. Examples of such carboxamides follow:

N-methylformamide N, N-dimethylformamide N-ethylformamide N, N,N-diethylformamide N-porpylformamide N, N, N-dipropylformamideN-butylformamide N, N-dibutylformamide The lower alkyl formamides andN-methyl-2-pyrrolidone of this invention are readily obtainable incommerce.

The lower alkyl formamide can be utilized in anhydrous state or when insolution in a suitable liquid solvent, usually water. Aqueous solutionsof N, N-dimethylformamide of about 58-95 weight percentdimethylformamide concentration are effective in inhibiting electrolessmetal plating of vinyl plastisoI-coated racks. N, N-diethylformamide iseffective in anhydrous or substantially anhydrous condition forinhibiting electroless metal plating of vinyl plastisoI-coated racks.The N-methyl-Z-pyrrolidone is also utilizable in the present inventionin anhydrous or substantially anhydrous state or when in solution in asuitable liquid solvent, usually water. Thus aqueous solutions ofN-methyl-2-pyrrolidone are effective for inhibiting electroless metalplating of vinyl plastisoI-coated plating racks at concentrations ofsuch compound of about 80 percent by weight and higher up to andincluding anhydrous state of the N-methyl-2-pyrrolidone.

Although the mechanism involved in the carboxamide treatment renderingthe vinyl plastisol-coated rack nonsusceptible to the electrolessdeposition of metal thereon is not known with certainty, one plausibleexplanation advanced is that the lower alkyl formamide orN-methyl-Z-pyrrolidone treatment results in a hardening and smoothing ofthe surface of the vinyl plastisolcoated rack to thereby preventadherence of the activator catalyst particles and to prevent absorptionof the stannous chloride sensitizer solution, when utilized.

DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE I by Weight N,N-dimethylformamide 91.7% H,0 8.3%

EXAMPLE II N, N-dimethylformamide 94.7% H,O 5.3%

EXAMPLE III N, N-dimethylformumide 85.8% H O 14.2%

EXAMPLE IV by Weight N, N-dimethylformamide 809% H O I9.l%

EXAMPLE V N, N-dimethylformamide 75.2% 11,0 24.8%

EXAMPLE VI N, N-dimethylformamide 72.4% 0 27.6%

EXAMPLE VII N, N-dimethylformamide 68.9% H 0 313% EXAMPLE VIII N,N-dimethylformamide 63.5% H O 36.5%

EXAMPLE IX N, N-dimethylformamide 58.8% H O 4l.2%

EXAMPLE x by Weight N, N-dimethylformamide 94.7% H 0 5.3%

EXAMPLE XI N-methyl-Lpyrrolidone H 0 0% EXAMPLE XIIN-methyl-2-pyrrolidone 80.41 H 0 [9.6%

nonconductive articles or-parts to be plated, for instanceplasticarticles or parts, e.g. articles or parts of ABS copolymer, are rackedon the'thus-treated rack.- The'surfaces of the racked articles, if notalready cleaned, arecleaned by immersion in a conventional nonsilicatedalkaline cleaner solution. When the articles or parts havehydro'phobic'surfaces, which is usually the situation with plasticarticles or parts, the surfaces are then converted from a hydrophobicstate to a hydrophilic state wherein the surfaces are readily receptiveto the aqueous solutions of the chemical reduction metal plating processor cycle. The conversion of the hydrophobic plastic surfaces tohydrophilic surfaces is preferably effected by contacting thehydrophobic surface with, usually by immersing such surfaces of theracked articles in, a conditioning or etchant solution comprising anaqueous acid solution containing concentrated sulfuric-acid (typicallyof 98 percent H SO,concentration) and chromic acid (Cr 0 and which mayalso contain phosphate ions. The conversion of the hydrophobic articlesurfaces-to hydrophilic surfaces can also be effected mechanically byrougheningthe hydrophobic surface, for instance by sanding, sandblasting'or abrading'the hydrophobic surface or surfaces. Exemplaryofthe conditioning solution is an aqueous solution of the followingcompositron:

oz./gal. 32 H, oz./gal.

After conversion of the hydrophobic surfaces to hydrophilic surfaces iscompleted the articles still on the same rack are rinsed with water.

The hydrophilic nonconductive or nonmetallic surfaces of the rackedarticles are then activated in conventional manner, by contacting thehydrophilic surfaces with, usually by immersing the surfaces in, asensitizer solution,usually a'stannous chloride-containing aqueous acidsolution containing, in addition to stannous chloride, HCl and water,followed by water rinsing. A typical sensitizer solution is thefollowing:

SnCl l0 g. HCl 40 ml. H O 1.000 ml.

The HCI was the analytic reagent grade. The sensitizer is utilized atroom temperature for 1-3 minutes.

The sensitized surfaces of the articles still on the same rack are thencontacted with an activator solution, usually by immersing the surfacesin the activator solution. The activator solution is usually a palladouschloride-containing aqueous acid solution containing, in addition topalladous chloride, HCI and water. Other noble metal ions, e.g. platinumor gold ions, are utilizable in the activator solution instead of theionic palladium. A typical activator solution has the followingcomposition:

PdCl l g. HCl l0 ml. H,O l gal.

The HCl was the analytic reagent grade. The above activator solution isused at room temperature, with one-half-lminute immersion times. Afteractivating is completed, the surface of the racked articles are thenwater rinsed.

Alternatively, the sensitizing step can be eliminated by combining thestannous chloride of the sensitizer and palladous chloride in onecomposition to form a colloidal catalyst solution containing colloidalpalladium metal particles dispersed in a liquid medium as disclosed inU.S. Pat. No. 3,0l L920 The racked plastic articles are immersed in orotherwise treated with the colloidal catalyst solution until theirsurfaces are activated for the subsequent electroless metal plating.

The racked activated articles are then 'electrolessly metal plated bycontacting the article surfac'es'with', usually by immersing thearticlesin a chemical reduction metal plating.

solution'in the usual manner. Exemplary of the chemical reductionmetalplating. solutions are chemical reduction copper platingsolutionsand chemical reduction'nickel plating,

solutions or baths. The articles are maintained in contact withthe'chemical reduction metal 'pla'ting'solution until a metal layer ofthe 'desired thickness is deposited on the 'articlesur faces, oruntil'the article-surfaces a're 'rendered electrically conductive.Typical chemical reduction aqueous copper and nickel plating solutionsfollow:

CHEMICAL R'EDUCTION COPPER PLATING BATH.

Ve'rsene T" isa trademarked material containing- EDTAandtriethanolamine.

CHEMICAL REDUCT'IONNICKEL' PLATING BATH Nickel chloride 30 Sodiumcitrate lUO Ammonium chloride 50 Sodium hypophosphite l0 Adjust pH to pH8-l0 with Bath Temperature l'- )0 F.

After the electroless metal plating iscomplet'ed, the articles stillonthe sa'r'nerack are then electroplated with; forexaniple', copper in theusual man'ner'A typical'electroplatihgbath for this purpose is an acidsulfate aqueous bath containing 20'0-300' ./1. of cu so,-5-H,0' andl5-40-g1/l. of free H-,so-, (66 Be). After this electroplating step, oneor more final electroplates, which may be decorative, are usuallyapplied over the first-mentioned metal electroplate. These finalelectrop'lates areordinarily thin layers and may be a layer ofbrightnickel followedby a layer of chromium thereover, or a layer ofduplex nickel with a layer if microcracked chromium thereover.

The electrically nonco'nducti've articles or parts metal plated'hereininclude, for example, plastic knobs for window crank handles ofautomobiles and garnish or decorative plastic moldings for automobiles.The plastic includes, for example ABS copolymer, i.e.acrylonitrile-butadiene-styrene co'polymer, and other polymers orplastics, e.g. polypropylene, polystyrene and polycarbonate.

in tests and experimental work conducted, N, N-dimethylfo'rmarnide wasfound to inhibit electroless metal plating of the vinylpla'stisol-coated plating rack after immersion of the rack in aqueoussolutions of the N, N-dimethylformamide of about 5895 weight percent N,N-dimethylformamide concentration. Aqueous solutions of higherconcentration of the N, N- dimethylformamide than 95 percent andsubstantially anhydrous N, N-dirnethylformamide, although inhibiting theelectroless plating of the rack, attacked the polyvinyl chloride of theplastisol-coating of the rack. Substantially anhydrous N,N-diethylformamide was effective in inhibiting electroless metal platingof the vinyl plastisol-coated rack, but an aqueous solution of percentby volume N, N-diethylformamide concentration was not effective ininhibiting the rack plating. Aqueous solutions of N-methyl-Z-pyrrolidoneof 80 volume percent and higher N-methyl-2-pyrrolidone concentrationwere found to be effective in inhibiting electroless metal plating ofthe vinyl plastisol-coated racks. Anhydrous N-methyl-2- pyrrolidone wasalso found to be effective in inhibiting electroless metal plating ofsuch racks. However 2-pyrrolidone was not effective in anhydrous stateor in aqueous solution of 95 volume percent 2-pyrrolidone concentrationand actually enhanced electroless metal plating of the racks.

Formamide, acetamide and methyl ethyl ketone were found not effectivefor inhibiting electroless metal plating of vinyl plastisol-coatedracks. Tetrahydrofuran was also found to be unsatisfactory forinhibiting such rack plating.

The tests also revealed that the N, N-dimethylformamide in aqueoussolutions of the N, N-dimethylformamide concentration set forthimmediately supra, the substantially anhydrous N, N-diethylformamide,the N-methyl-Z-pyrrolidone in aqueous solutions of theN-methyl-Z-pyrrolidone concentration set forth immediately supra, andanhydrous N-methyl-2-pyrrolidone, were effective in inhibitingelectroless metal plating of the vinyl plastisol-coated racks when theactivating was effected by immersing the racked plastic articles in acolloidal catalyst solution containing colloidal palladium metalparticles dispersed in water. In the absence of the contacting ofplastisol-coated racks with such compounds, the racks which were in anintermediate stage of life and susceptible to electroless metal platingwere metal plated during the electroless plating step, when theactivating waseffected using the colloidal catalyst solution containingthe colloidal palladium metal particles dispersed in water.

While the novel features of the invention have been dis closed hereinand are specified in the annexed claims, it will be understood thatvarious omissions, substitutions and changes may be made by thoseskilled in the art without departing from the spirit of the invention.

What is claimed is:

l. A process for the metal plating of electrically nonconductivearticles on plastisol-coated plating racks, which comprises:

a. contacting the plastisol-coated rack characterized by beingsusceptible to electroless metal plating, prior to racking thereon theelectrically nonconductive articles destined to be plated, with a liquidmaterial selected from the group consisting of a lower alkyl formamide,N- methyl-Z-pyrrolidone, and mixtures thereof for a period sufficientsufficient to render the rack substantially nonsusceptible toelectroless plating of metal thereon during a subsequent chemicalreduction metal plating step;

b. racking at least one electrically nonconductive articles destined tobe electrolessly metal plated on the thustreated rack;

c. activating hydrophilic surfaces of the racked nonconductive article;and

d. electrolessly metal plating the racked activated article bycontacting the article with a chemical reduction metal plating solutionuntil a metal plating of a desired thickness is deposited on the articlesurface;

e. the electroless metal plating of the racked article occurring withoutany substantially metal plating of the rack.

2. The process of claim 1 wherein the racked electrically nonconductivearticle is sensitized prior to being activated.

3. The process of claim 2 wherein the selected material is N,N-dimethylformamide.

4. The process of claim 2 wherein the selected material is N-methyl-Z-pyrrolidone.

5. The process of claim 1 wherein the lower alkyl formamide is of theformula:

wherein the Rs each represent a l-4C alkyl group or a hydrogen atom withat least one R being a l-4C alkyl group.

6. The process of claim 3 wherein the N,N-dimethylformamide is anaqueous solution of about 58-95 weight percent N ,N -dimethylformamideconcentration.

7. The process of claim 4 wherein the N-methyl-Z-pyrrolidone is in anaqueous solution of at least about weight percent N-methyl-Z-pyrrolidoneconcentration.

8. A no rerack process for the metal plating of plastic articles onvinyl plastisol-coated racks, which comprises:

a. contacting the vinyl plastisol-coated rack characterized by beingsusceptible to electroless metal plating, prior to racking the plasticarticles destined to be plated, with a liquid material selected from thegroup consisting of a lower alkyl formamide, N-methyl-2-pyrrolidone, andmixtures thereof, for a period sufficient to render the racksubstantially nonsusceptible to electroless plating of metal thereonduring a subsequent chemical reduction metal plating step;

b. racking plastic articles destined to be metal plated on thethus-treated rack;

c. converting hydrophobic surfaces of the racked plastic articles tohydrophilic surfaces receptive to chemical reduction metal platingprocess aqueous solutions;

d. activating the hydrophilic surfaces of the racked plastic articles;

e. electrolessly metal plating the racked activated plastic articlesurfaces by contacting the articles with a chemical reduction metalplating solution until the article surfaces are rendered electricallyconductive; and

f. without reracking the electrolessly metal plated article,electroplating a metal layer onto the conductive surface of the articleswhile still on the same rack;

g. the electroless metal plating of step (e) and hence theelectroplating of step (f) occurring without any substantial metalplating of the rack.

9. The process of claim 8 wherein the racked plastic articles aresensitized prior to being activated.

10. The process of claim 9 wherein the selected material isN,N-dimethylformamide.

11. The process of claim 9 wherein the selected material isN-methyl-Z-pyrrolidone.

12. The process of claim 8 wherein the lower alkyl formamide is of theformula wherein the Rs represent a l-4C alkyl group or a hydrogen atomwith at least one R being a l-4C alkyl group.

13. The process of claim 9 wherein the electroless metal plating iselectroless copper plating and the chemical reduction metal platingsolution is a chemical reduction copper plating solution.

14. The process of claim 9 wherein the electroless metal plating iselectroless nickel plating and the chemical reduction metal platingsolution is a chemical reduction nickel plating solution.

15. The process of claim 9 wherein the contacting of the rack with theselected liquid material is effected by immersing the rack in a liquidbath thereof.

16. The process of claim 10 wherein the N,N-dimethylformamide is in anaqueous solution of about 58-95 weight N,N- dimethylformamideconcentration.

17. The process of claim 11 wherein the N-methyl-Z-pyrrolidone is in anaqueous solution of at least about 80 weight percentN-methyl-Z-pyrrolidone concentration.

18. The process of claim 8 wherein the hydrophobic surfaces of theracked plastic articles are converted to the hydrophilic surfaces byimmersing the racked articles in a conditioning solution comprising anaqueous acid solution containing concentrated sulfuric acid and chromicacid for a period sufficient to effect such conversion.

19. The process of claim 8 wherein the electroplating of the rackedarticles is of a copper electroplate layer onto the conductive surfacesthereof.

20. The process of claim 19 further characterized by electroplating oneor more final metal electroplate layers over the copper electroplatelayer while the articles are still on the same rack.

21. A preconditioned vinyl plastisol-coated rack for holding articlesdestined to be metal plated and characterized by being substantiallynonsusceptible to electroless plating deposition of metal thereon whileimmersed in a chemical reduction metal plating solution, the rack havingbeen conditioned by contacting the same with a liquid material selectedfrom the group consisting of N,N-dimethylformamide,N-methyl-Z-pyrrolidone, and mixtures thereof for a time sufficient torender the rack substantially nonsusceptible to electroless plating- 5,25 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO.3,619,243 Dated November 9; 1971 Inventor(s) Frank A. Brindisi, Jr. andTheophil J. Wieczorek It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

r- Column 1, line 8, "articles" should read --article--. I C'olumn 2,line 3, "or" (second occurrence) should read --to--; line 10, after"ing" the letter --o-- should be deleted; line 70, after "aqueous'--formamide-- should be deleted and the following should be insertedafter "aqueous" and before "both" --solution. When the lower alkylformamide is N,N-diethylformamide,'--; line 74, "presented" should read--represented--. Column 3, line 13, "N,N,N-diethylformamide"' shouldread --N,N-diethylformamide--; line 15, "N,N,N-dipropylformamide" shouldread --N,N-dipropy1formamide--. Column 4, line 36, "313%" should read--3l.lZ,--; line 58, "N,N-dimethylformamide" should read--N,N-diethylformamide--. Column 7, line 52, "articles" should read--article--.

and se led this: Zzh day of Nov 1972.

A lim t:

WIMP?) ZQFLFTC -1 37}? ,JR PFOBERJJ GOTTSCHALK A was ting Office 1'"Commissioner of Pa boots

2. The process of claim 1 wherein the racked electrically nonconductivearticle is sensitized prior to being activated.
 3. The process of claim2 wherein the selected material is N, N-dimethylformamide.
 4. Theprocess of claim 2 wherein the selected material isN-methyl-2-pyrrolidone.
 5. The process of claim 1 wherein the loweralkyl formamide is of the formula: wherein the R''s each represent a1-4C alkyl group or a hydrogen atom with at least one R being a 1-4Calkyl group.
 6. The process of claim 3 wherein the N,N-dimethylformamideis an aqueous solution of about 58-95 weight percentN,N-dimethylformamide concentration.
 7. The process of claim 4 whereinthe N-methyl-2-pyrrolidone is in an aqueous solution of at least about80 weight percent N-methyl-2-pyrrolidone concentration.
 8. A no rerackprocess for the metal plating of plastic articles on vinylplastisol-coated racks, which comprises: a. contacting the vinylplastisol-coated rack characterized by being susceptible to electrolessmetal plating, prior to racking the plastic articles destined to beplated, with a liquid material selected from the group consisting of alower alkyl formamide, N-methyl-2-pyrrolidone, and mixtures thereof, fora period sufficient to render the rack substantially nonsusceptible toelectroless plating of metal thereon during a subsequent chemicalreduction metal plating step; b. racking plastic articles destined to bemetal plated on the thus-treated rack; c. converting hydrophobicsurfaces of the racked plastic articles to hydrophilic surfacesreceptive to chemical reduction metal plating process aqueous solutions;d. activating the hydrophilic surfaces of the racked plastic articles;e. electrolessly metal plating the racked activated plastic articlesurfaces by contacting the articles with a chemical reduction metalplating solution until the article surfaces are rendered electricallyconductive; and f. without reracking the electrolessly metal platedarticle, electroplating a metal layer onto the conductive surface of thearticles while still on the same rack; g. the electroless metal platingof step (e) and hence the electroplating of step (f) occurring withoutany substantial metal plating of the rack.
 9. The process of claim 8wherein the racked plastic articles are sensitized prior to beingactivated.
 10. The process of claim 9 wherein the selected material isN,N-dimethylformamide.
 11. The process of claim 9 wherein the selectedmaterial is N-methyl-2-pyrrolidone.
 12. The process of claim 8 whereinthe lower alkyl formamide is of the formula wherein the R''s represent a1-4C alkyl group or a hydrogen atom with at least one R being a 1-4Calkyl group.
 13. The process of claim 9 wherein the electroless metalplating is electroless copper plating and the chemical reduction metalplating solution is a chemical reduction copper plating solution. 14.The process of claim 9 wherein the electroless metal plating iselectroless nickel plating and the chemical reduction metal platingsolution is a chemical reduction nickel plating solution.
 15. Theprocess of claim 9 wherein the contacting of the rack with the selectedliquid material is effected by immersing the rack in a liquid baththereof.
 16. The process of claim 10 wherein the N,N-dimethylformamideis in an aqueous solution of about 58-95 weight N,N-dimethylformamideconcentration.
 17. The process of claim 11 wherein theN-methyl-2-pyrrolidone is in an aqueous solution of at least about 80weight percent N-methyl-2-pyrrolidone concentration.
 18. The process ofclaim 8 wherein the hydrophobic surfaces of the racked plastic articlesare converted to the hydrophilic surfaces by immersing the rackedarticles in a conditioning solution comprising an aqueous acid solutioncontaining concentrated sulfuric acid and chromic acid for a periodsufficient to effect such conversion.
 19. The process of claim 8 whereinthe electroplating of the racked articles is of a copper electroplatelayer onto the conductive surfaces thereof.
 20. The process of claim 19further characterized by electroplating one or more final metalelectroplate layers over the copper electroplate layer while thearticles are still on the same rack.
 21. A preconditioned vinylplastisol-coated rack for holding articles destined to be metal platedand characterized by being substantially nonsusceptible to electrolessplating deposition of metal thereon while immersed in a chemicalreduction metal plating solution, the rack having been conditioned bycontacting the same with a liquid material selected from the groupconsisting of N,N-dimethylformamide, N-methyl-2-pyrrolidone, andmixtures thereof for a time sufficient to render the rack substantiallynonsusceptible to electroless plating deposition of metal thereon whilein contact with the chemical reduction metal plating solution.
 22. Therack of claim 21 wherein the selected material is N,N-dimethylformamide.23. The rack of claim 21 wherein the selected material isN-methyl-2-pyrrolidone.